Electronic oscillator



Sept. 22, 1936. E, HQLLMANNg* 2,054,816

ELECTRONIC OS C ILLATO-E'J Filed July a', 1930. v

'ily d j] 'EHI-l'l'l-M- Venors- 4Hain/1.5 [nk/7 Hallman/7 Patented Sept. 22, 1936 PATENT OFFICE vELECTRONIC OSCILLATOR Hans Erich Hollmann, Berlin-Charlottenburg,

' Germany, assigner, by mesne assignments, to American Telephone and Telegraph Company, a corporation of New York Applicatitnjiuly s, 1930, serial No. 466,524

i 'In'. Germany July-10, 1929 6l Claims. y(Cl. Z50- 36) My invention relates to improvements in' ultra high frequencyelectronicoscillators Y, and -more particularly to oscillators of the Barkhausen type. Y

In the generation of short electric waves by means of the customary regenerative arrangements there is a lower limit of wave length attainable occasioned by the fact that the time of transit of the electrons within the tube can no longer be ignored as compared With the period of oscillations determined by the constants of the oscillatory circuits. Consequently the ordinary regenerative coupling conditions as far as they concern the phase relations of thevgrid and anode alternating potentials are nol longersuflicient. For commercial tubes it has been found that the lower limit of the wave length obtainable in such arrangements is about `1 meter.

Shorter waves can be vgenerated by what is :called the braking field method according to Barkhausen and Kurz in which the frequency is mainly determined by the time of transit of the electrons in the interelectrode space. In contrast with the ordinary method of operating a three electrode tube, the grid potential ishighly positive and the plate potential is negative. wave lengths produced are found to be'prir'narily determined only by the dimensions of the tubeA and the applied potentials and are not greatly inuenced by the constants of the associated circuits.

The object of my invention isto .provide an improved circuit for transmitting as well as for receiving utilizing the above method, and which f insures increased efficiency and ease of operation. ,Y

A more specic object of the` invention is to provide means in connection with an electronic.v

oscillator of the type to which reference-'has been made to impress a note -of different; fre-.` quency upon the highV frequency oscillations for Y purposes of transmission and reception. v

This and further objects of my invention will become more apparent by the following descrip-Y tion taken with reference toV the laccompanying drawing, in which I have illustrated one form of embodiment of the invention.'r

I wish it to be understood howeverthat the .In Fig. 1 I have shown, for purposesof illus- The' Voscillating system Z, as shown in Fig. 2. The two embodiment of the invention shown vin the draw-` Fig. 2 shows a similar'cireuit to` Fig. 1, with an 5 1` oscillatory system associated with the oscillator tube for purposes of practical utilization of the oscillations.

Figs. 3 and 4 are theoretical curves illustrating the physical phenomena taking place in a circuit according to Fig. 2 which are made use of in accordance with the spirit of the present invention.

Fig. 5 illustrates a circuit arrangement adaptable for transmission as well as for reception embodying the novel improvements.

Similiar reference characters refer to similar elements throughout the different views of the drawing.

Referring more particularly to Fig. ,1, I have shown an electronic tube of the thermionic type comprising a heated cathode c, grid electrode g, and anode a. The cathode is maintained at electron emitting temperature by means of a heating battery En. A positive potential with respect to the cathode is applied to the grid electrode by a grid battery Eg, and a negative potential with respect to the cathode is applied to the anode by a battery Ea in combination with a potentiometer p, which latter serves to adjust a proper-value of anode potential'. VAs explained above the electrons emitted from the cathode and attracted by the positive grid will pass through the meshes of the grid and will' be reversed by the counter-acting field of the negative anode whereby a kind of to` and fro movement of the electrons about the grid takes place at a frequency dependent on the dimensions of the tube and the operating potentials applied, as may be readily understood.

In this manner high frequency oscillations may be easily produced having a Wave length less than I meter down to fractions of a centimetro.

In order vto utilize these oscillations it is customary to associate with the tube a parallel wire Wires are connected by a bridge comprisinga blocking condenser of Ylarge capacity and two open wires l which latter may serve for radiation of the oscillations into space. For thispurpose the length of the wires Z has to be equal to the 50 wave length, or a multiple thereof, of the oscillations produced within the tube. Furthermore it is necessary that the distance d of the bridge from the tube electrodes be a multiple of the wave length. In order to block the voltage sources Eg tive grid and that no electrons at all would reachflflthe negative anode. It is observed, however, and, may be verified by experiment that nevertheless' an anode current occurs, which'iiows ina negative direction, that is, in a directionopposite to the anode voltage, which anode current-is due to the' high frequency to and fro movement of the electrons about the grid.

This negative anode current which' flows trodes. In the latter case the negative anode current becomes of particular importance in connection with changes of the anode voltage Ea.

I have shown in Fig. 4 the relation between anode current and anode voltage. The curve A' which corresponds to the operating point A according to' Fig. 3 illustrates. the-gradual decrease of the current-With increasing negative anode potential, that is for the case that the oscillatory lwire system Z is considerably out of tune with the oscillating. frequency of the electrons within the tube? These'conditions however change with the parallel-.Wiresystem being tuned to a point directly beforethesettingiin of the frequency reaction,

suchaspointBonC -according to Fig. 3, to which correspond-fthe curves of B and C in Fig. 4. Theselattencurves-also show at iirst a gradual l'.pdecr-easefoiY the anode current Ia until an account against the anode potential or which, in other words, charges the anode battery, is in general anindication of the occurrence ofthe electronic oscillations. current may be given in that part of the electrons moving forth and back about the grid, as-

sume an additivekinetic energy and are forced to the anode beyond the plane of zero potentialfwithin which ordinarilyxthe electrons are reversed. With increasing negative anode potential Ythis plane of zero potential moves more 'and more away Anlexplanation for the flow ofA this from the anode whereby the number of electrons reaching the anode and consequently the negativeY anode current decreases gradually'.

of the frequency increase of the exciting electron If.l the tuningcondition ofthe oscillatory system 4is Y moved further away from the critical resonance point for the. frequency reaction (point C according to Fig. 3) it is seen from curve C' that a higher change of. theveXciting frequency and accordl inglyiahigher anode potentialwill be necessary inprdertoy produce -the frequencyY reaction.`

action the anode current'decreases again gradual- These simple conditions change considerably if the gridand'anodeof the tube are connected with 'an oscillatory system,'such as is shown in'Fig. 2.'y In such a circuit, the movement ofthe .electrons is no longerlexclusively determinedby the stationary interelectrode fields corresponding to the operating voltages, but it is subject also to the vin- Vfiuences ofthe alternating voltages induced 'initlie oscillatory systemand superimposed upon the' directV current.potentialsapplied to the electrodes.

latory circuit,Y which phenomenon inV analogy to the well l. known amplitude feed back or reaction.

may be described as frequencyregeneration. Y

Concomitant' with these-wave changes dueto ythe frequency reaction an increase ofthe oscillating energy takes place in that by the controllingH action .of the'alternating fields a larger-number Lk ofelectrons isforced to take part in the back'and".

forth movements.

Thisf is observed by an :im-1

mediate and very rapid rise of the Ynegative anode@4 current such as is seen from the curve of Fig. 3.

This curve, `whichfshows the fnegative 'anode current as a function'ofy the -tuning of the'oscillatory system is obtained by moving the con-V densersbridgeto different-distances d from-the tube electrodes Immediately after passing the point B the frequency'reaction sets in and alfrapid risefof the vanode currentltakes` place.l

The setting in of the frequency reaction and the increase of the anode current/associatedY therewith is .not only dependent on thetuning of the-oscillatory system,.but also on the electron frequency within the'tube'- The setting in of the frequency reaction willf-lr'nove'to higher frequencies, the high-er the originalffrequency ofthe electron movements. This provides an opportunity to control the frequency reaction veitherfby detuning the oscillatory circuit or by changing'theAv operatingconditions, as, for example, by varyingv .the-direct'current potentials applied'to theelec-l ly with increasing anodevoltage.r

The-rise of the anodecurr'ent-as seen from the portions c and b'; of the-curves B' and C With increasingnegativeor. in general with decreasing positive anode potentialillustrates that this braking field Varrangement acts` as a negative resist- Y anceowing -t'o thereaction of-the anode potential upon thetuningconditions vof the system:

Similar-devices, such as anv electric arc, the

dynatron'vacuum tube and others, exhibiting' aV negative resistance characteristic; i.- e. rising current Wi-th'falling voltage, are well known in the l art and areused-for exciting an oscillatory circuit and sustaining thefree natural oscillations cf suchfcircuit.. The' Aresistance is identical to a source of" energy compensatingfor the'losses of the circuit and thus maintaining undamped oscillation.`

In accordance with the present inventionthis phenomenon ismade use of for producing a current off: diierentffrequencyto be utilized .in connection with the Yhigh frequency oscillations forV the purpose 'off practical application of these ultra-high frequency currents, such as for transmissionand receiving of 'wireless signals. This is shown in Fig. 5 which'diifers from Fig. 2 in that an oscillatory circuit o of the-ordinary type comprising Va concentrated inductance and capacity in parallelislincluded in thefanode leads. If at the same time'l the operating conditions, that is the tuning of the parallel wireY system Z (by properly choosing distance@ and the proper adjustment of the Voperatingianode voltage Ea are such `that the tube presents a negative resistance characteristic (operatingirange b' or c' according to Fig.'4)',"such'as set forth above, thecircuit owill4 oscillate in a frequency equal to its own natural7 frequency, which may be chosen at will by proper tuning-in. the manner Well known in the art.

If the system'is used as an oscillator for transmission and if the oscillations produced by the the oscillations may be observed by means of a telephone receiver T included in the anode lead. In this case the oscillations produced by the oscillatory circuit o are impressed upon the high frequency oscillations produced by the tube system or, according to common language, the high frequency electronic oscillations are modulated in accordance with the frequency equal to the natural frequency of the circuit o. This makes a system according to Fig. 5 suitable for use as a transmitter for wireless signals.

If the same circuit according to Fig. 5 is to be used as a receiver, care must be taken that the open wires Z as well as the distance d are properly tuned to the frequency radiated by the transmitter. Furthermore in this case the tube is so operated, that it produces only very weak oscillations (for instance by decreasing the heating current). Whenever incoming waves impinge upon the wires l', the oscillations are increased and the circuit o in this case too acts by a kind of self modulation by which an effect similar to the well known super regenerative action in radio receivers is obtained, producing'a considerable increase of the receiving current intensity.

I wish it to be understood that I do not desire to be limited to the exact details of construction shown and described for obvious modifications will occur to a person skilled in the art.

I claim:

1. In combination with a high frequency system, an electronic oscillator comprising an electron discharge tube, having electron Aemitting cathode, anode, and auxiliary grid electrode, means to apply suitable positive and negative potential to said grid and anode electrodes, respectively, to produce ultra high frequency oscillations, a utilization circuit for said ultra high frequency oscillations, connected' to said discharge tube, means whereby the discharge path within said tube exhibits negative resistance characteristic, and an oscillatory circuit comprising an inductance and capacity in parallel connected to said tube to be excited in its own natural frequency by said negative resistance to impress a modulating note of substantially different frequency upon said high frequency oscillations.

2. In combination with a high frequency system an electronic oscillator comprising an electron discharge tube having a cathode, anode, and grid electrode, means to apply suitable positive and negative potential to said grid and anode, respectively, for producing ultra high frequency oscillations, a two-Wire oscillating system connected to said grid and said anode, said oscillating system being so adjusted in respect to the natural frequency of the electron movements, that the discharge path of the tube exhibits negative resistance characteristic, and an oscillatory circuit comprising an inductance and a capacity in multiple connected to said tube to be excited in its natural frequency by said negative resistance to impress a modulating note of substantial- 1y different frequency upon said ultra high frequency oscillations.

3. In combination with a high frequency system an electronic oscillator comprising an electron tube having cathode, anode and'grid electrode, means to apply suitable positive and negative potential to said grid and anode, respectively, for producing ultra highr frequency oscillations, a two-wire oscillatory system, connected to said anode and said grid, means to adjust the length of said oscillating system in respect to the natural frequency of the interelectrode electron movements in such manner that the tube operates within its range exhibiting negative resistance characteristic and an oscillatory circuit consisting of an inductance and capacity in parallel connected to said tube to be excited in its natural frequency by said negative resistance to impress a modulating note of substantially lower frequency upon said ultra high frequency oscillations.

4. In an ultra high frequency system, a three electrode electron tube having cathode, grid and anode, means for applying positive potential to said grid with respect to said cathode, means for applying a potential to said anode at least as negative as that of said cathode, whereby high frequency oscillations are produced, a two-Wire oscillatory system connected to said grid and said anode, a condenser bridge for adjusting the length of said wire system, and an oscillatory circuit consisting of an inductance and capacity in parallel and inserted in series with said second means, said potentials being furthermore so adjusted as to secure negative resistance characteristic -of said tube to excite said auxiliary circuit in its own frequency to impress a modulating note upon said high frequency oscillations.

5. In a high frequency system in accordance with claim 4, according to which the natural frequency of saidoscillatory circuit is within the audible range and a translating device connected in the circuit for rendering the high frequency oscillations audible.

6. In a high frequency system, a three electrode electron tube having cathode, grid and anode, means for applying positive potential to said grid with respect to said cathode, means for applying negative potential to said anode with respect to said cathode, whereby ultra high frequency oscillations are produced, a two-Wire oscillating system connected to said grid and said anode, a condenser bridge for adjusting the length of said system, said potentials and the tuning of said wire system being so related that the tube cperates within its operating range exhibiting negative resistance characteristics and an oscillatory circuit consisting of an inductance and a capacity in parallel inserted in series with said first means for applying potential to impress a modulating note of substantially different frequency upon said high frequency oscillations.

HANS ERICH HOLLMANN. 

